This invention relates generally to ink compositions, and more specifically to viscous ink compositions having incorporated therein, for example, dimer acids. In one embodiment, the ink compositions of the present invention are comprised of a sponge component such as a polymer and dispersed therein pigment particles, dimer acids, and other components as illustrated herein including dyes, which inks can, for example, be coated onto various substrates inclusive of polyesters from a single solvent process to enable the preparation of, for example, multistrike typewriter ribbons useful in imaging and printing processes. Additionally, in a further aspect of the present invention there are provided improved processes for affecting the preparation of multistrike typewriter ribbons. These processes are simple in design, and economically attractive; and furthermore, the solvent selected can be easily recovered in a high purity of about 99 percent. Moreover, the aforementioned processes enable multistrike typewriter ribbons with controlled pore size and density permitting, for example, the fabrication of ribbons especially useful with the high viscosity inks disclosed hereinafter. In addition, a further advantage associated with the inks of the present invention resides in the elimination of an adhesive layer between the supporting films such as Mylar polyesters and the sponge containing the ink dispersed therein.
Multistrike typewriter ribbons are known, reference for example U.K. Patent Publication No. 2,118,584, the disclosure of which is totally incorporated herein by reference. This publication discloses overlapping, overstrikeable typewriter ribbons or print ribbons, especially useful with daisy wheel typewriters and printers. It is indicated in this publication that overstrike ribbons consisting of a thin carrier film onto which an ink releasing coating is applied in the form of a matrix consisting of a plastics binder and an ink paste dispersed therein are known. The ink paste selected is generally comprised of an oil that is substantially incompatible with the plastic of the matrix and the colored pigments. As illustrated in this publication, an important requirement of overstrike ribbons is that at each character strike the same amount of ink paste should emerge from the ink release coating at every location on the ribbon. Typewriter ribbons are prepared in accordance with the teachings illustrated in the British publication by solution coating a mixture of a binder having an ink therein onto a carrier film comprised of, for example, polyesters, polyethylenes, polypropylenes, or polyamides. These processes select the known two solvent system, for example, a combination of methyl ethyl ketone, which has a boiling point of 80.degree. C. and thus functions as a solvent for the binder selected, and toluene with a boiling point of 111.degree. C. Disadvantages associated with the known two solvent systems for obtaining multistrike typewriter ribbons is the requirement that, for example, the toluene and methyl ethyl ketone components usually selected be removed by heating the formulated ribbons at a temperature equal to or greater than the boiling point of the solvent. As the solvent is removed, the polymer binder and ink, which are incompatible with each other, form a two phase system consisting of a continuous, foam or sponge-like matrix with the binder material adhering to the carrier film and the ink uniformly dispersed in the pores of the sponge. The pore size and pore density, that is for example the number of pores per unit area, are design factors which can influence the performance of the ribbon in a given printing system. Generally, a temperature of about 150.degree. C. is needed to remove the toluene, and this temperature is much higher than the glass transition temperature of the polymer matrix. For example, a commercially utilized component, Union Carbide's VYHH a vinyl chloride/vinyl acetate copolymer, has a glass transition temperature Tg of 72.degree. C. The aforementioned high temperature treatment and the air velocity of the dryer selected causes local imbalances in the ink/polymer ratio resulting in undesirable ribbons with an inhomogeneous structure. Further, upon depletion of the solvent, methyl ethyl ketone from the coating mixture, the polymer binder remains in the nonsolvent toluene, and is thus converted to a gelled state creating difficulties in formulating ribbons with controlled pore sizes and desirable pore densities. For example, the typewriter ribbon resulting usually has very few large pores, that is from about 5 to about 20 pores per 100 square micrometer of from about 5 to about 15 micrometers in size as compared to the needed about 50 to about 80 pores per 100 square micrometer of 1 to about 3 micrometers in size diameter. The large pore size generally causes a quick ink release upon impact, and the ribbon possesses a poor overstrike capability. With the process of the present invention wherein there is selected a single solvent system, the ink is comprised of the components as illustrated, the aforementioned problems are substantially eliminated.
Additionally, there is illustrated in U.S. Pat. No. 4,515,489 a print transfer ribbon for use with high velocity printing devices such as print wheels. Specifically, there is disclosed in this patent an overstrike ribbon with multiple overstrike capacity, at least a five fold overstrike capacity, which comprises a synthetic resin carrier foil provided on a surface adapted to confront a paper substrate with a color transfer layer, the color transfer layer consisting of the synthetic resin binder matrix, and dispersed in this matrix interconnecting droplets of an oil based coloring matter which can be partly extruded by impact of a typeface there against the substrate. The oil base coloring material selected contains at least one oil dispersable coloring agent or pigment, at least one filler, and at least one wetting agent.
Other prior art of interests includes U.S. Pat. No. 3,440,083 relating to pressure sensitive foils obtained from a coating containing a plastic resin and an opacifier compound; Japanese Ricoh Patent Publication 59-5088 describing an ink resin comprised of a film base, an adhesive layer and an ink layer with ink particles and a binder; IBM Technical Disclosure Bulletin Abstract, Vol. 15, No. 2, July 1972, which illustrates a ribbon support film coating comprised of a resin blend of polyesters, Teflon.RTM., and glycerol, and that the formulation is applied from a methyl ethyl ketone solvent; and Japanese No. 58114-991-A which discloses an electrorecording stencil paper comprised of a polyurethane resin and carbon black, and wherein the paper is prepared by dispersing carbon black in a solvent solution of a polyurethane resin, examples of solvents being methyl ethyl ketone, toluene and dimethyl formamide. In contrast, the ink coating compositions of the present invention are comprised of, for example, dimer acids and pigment particles.
Although the typewriter ribbons and ink formulations disclosed in the prior art are suitable in many situations for their desired purposes, there remains a need for new inks. Also, there is a need for high viscosity inks useful in imaging and printing processes. Furthermore, there is a need for highly viscous inks containing therein dimer acids, trimer acids, or mixtures thereof. There is also a need for simple economically attractive processes that will enable the formulation of multistrike typewriter ribbons. Furthermore, there is a need for the formulation of multistrike typewriter ribbons wherein the disadvantages associated with the two solvent system process of the prior art are eliminated, and wherein there is selected only one solvent. Also, there is a need for processes enabling multistrike typewriter ribbons wherein the polymer selected maintains its characteristics and does not convert to a gelatin stage during and upon completion of removal of the solvent from the coating mixture. Moreover, there continues to be a need for processes for multistrike typewriter ribbons wherein the ribbon resulting has a substantial number of pores with excellent pore density, and relatively uniform pore size.
There also remains a need for a simplified coating process and the recovering of the solvents selected for the aforementioned process without the necessity of having to separate two or more solvent mixtures selected in many of the prior art processes, and in several commercial processes for formulating typewriter multistrike ribbons. Moreover, there is a need for processes that will enable ribbons that can be selected for incorporation into various printers and typewriters using different impact forces and dwell times of the character as it impinges on the back of the ribbon by, for example, varying the ink viscosity and the polymer to ink ratio.